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public static void testForProblem() {
// 一些朋友在向循环里向列表增加对象的时候
// 经常忘记初始化,造成最终加入的都是同一个对象
List<MyObject> list = new ArrayList<MyObject>();
MyObject obj = new MyObject();
for (int i = 1; i <= 5; i++) {
obj.setName("Name" + i);
list.add(obj);
}
// 里面的数据都是最后一个
showList(list); // [Name5, Name5, Name5, Name5, Name5]
// 正确的做法
List<MyObject> list2 = new ArrayList<MyObject>();
MyObject obj2 = null;
for (int i = 1; i <= 5; i++) {
obj2 = new MyObject();
obj2.setName("Name" + i);
list2.add(obj2);
}
showList(list2); // [Name1, Name2, Name3, Name4, Name5]
}
/**
* 显示List里面的数据。
*
* @param list
*/
private static void showList(List list) {
System.out.println(Arrays.toString(list.toArray()));
}
}
class MyObject {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
/**
* 重写toString方法,输出name
*/
public String toString() {
return name;
}
public void add(int index,
E element)
{
rangeCheckForAdd(index);
ensureCapacity(size+1); // Increments modCount!!
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
elementData[index] = element;
size++;
}
public void ensureCapacity(int minCapacity)
{
modCount++;
int oldCapacity = elementData.length;
if (minCapacity > oldCapacity) {
Object oldData[] = elementData;
int newCapacity = (oldCapacity * 3)/2 + 1;
if (newCapacity < minCapacity)
newCapacity = minCapacity;
// minCapacity is usually close to size, so this is a win:
elementData = Arrays.copyOf(elementData, newCapacity);
}
}
int oldCapacity = elementData.length;
if (minCapacity > oldCapacity) {
Object oldData[] = elementData;
int newCapacity = (oldCapacity * 3)/2 + 1;//增加空间
if (newCapacity < minCapacity)
newCapacity = minCapacity;//如果增加的空间还不能满足,则用新的空间(可能是针对ADD(list)的情况)
elementData = (E[])new Object[newCapacity];
System.arraycopy(oldData, 0, elementData, 0, size);
}